The present invention relates to radio/microwave power measurement devices and in particular to an extremely compact high-power measurement device.
Radiofrequency power meters are used to measure the power of a radiofrequency signal transmitted to an antenna or other load (forward power) as well as to measure reflected power back from the antenna or load (reflected power) such as may provide an indication of a voltage standing wave ratio (VSWR), power consumption or the like. These dual measurements allow determination of the actual amount of power delivered to the load and permit tuning and adjustment of the load or source for optimal power transfer. The term radiofrequency is used herein shall be considered to embrace high-frequency (HF), very high frequency (VHF), ultrahigh frequency (UHF) and microwave frequency signals.
Three common designs for radiofrequency power meters are those which employ waveguides (typically for microwave frequencies) and coaxial or microstrip transmission lines (typically for HF, VHF and UHF frequencies) placed in series between the power transmitter and the load.
In the former design, a primary waveguide is coupled to a secondary waveguide through two ports located to couple signals from the primary waveguide to the secondary waveguide at points with a 90-degree phase difference (one quarter wavelength) at the conducted signal frequency. The outputs of the secondary waveguide at opposite ends will individually isolate the forward and reflected power allowing these two different quantities be measured, for example, with a diode sensor.
In the latter design, signals from the primary transmission line are received by an a transmission line physically analogous to the secondary waveguide, again through openings separated by a 90-degree phase difference (one quarter wavelength) along the primary transmission line. Outputs from the opposite ends of the secondary transmission line isolate the forward and reflected power.
The process of isolating forward and reflected power in both of these designs requires analyzing structures (secondary waveguides or secondary transmission lines) having a length in excess of a quarter wavelength of the measured frequency. For UHF frequencies, for example, this can require constructing carefully tuned structures having a length many centimeters long. Power meters intended for different frequencies can require wide range of different analyzing structures.